青海省乌兰地区肯得隆富钛铁矿镁铁-超镁铁质岩体的岩石与矿石成因  

Petrogenesis and ore genesis of the ilmenite-rich Kendelong mafic-ultramafic intrusion in Wulan,Qinghai

作　　者：康珍[1,2,3] 姜常义[3,4] 凌锦兰[3] 赵彦锋[3] 宋艳芳[3] 周伟[3] 

机构地区：[1]中国科学院矿产资源研究重点实验室、中国科学院地质与地球物理研究所,北京100029 [2]中国科学院大学,北京100049 [3]长安大学地球科学与国土资源学院,西安710054 [4]西部矿产资源与地质工程教育部重点实验室,西安710054

出　　处：《岩石学报》2015年第8期2193-2210,共18页Acta Petrologica Sinica

基　　金：青海省地质勘查基金项目(2012209);国家自然科学基金项目(41030424)联合资助

摘　　要：肯得隆镁铁-超镁铁质岩体位于青海柴达木盆地北缘欧龙布鲁克微陆块中。岩体为半隐伏岩体,地表零星出露。岩体岩石类型丰富,有蛇纹岩、单辉橄榄岩、二辉橄榄岩、橄榄二辉岩、橄榄单辉岩、橄榄苏长辉长岩、橄榄角闪辉长岩、角闪辉长岩、蚀变辉长岩、斜长岩。辉长岩、辉石岩中见稀疏浸染状、星点浸染状钛铁矿。钛铁矿含量以5%~10%为主,个别含量可达10%~20%,具海绵陨铁结构,属岩浆晚期矿化作用产物。岩体中辉长岩锆石U-Pb年龄为491±3Ma(MSWD=0.7)。岩体岩石的化学组成属于拉斑玄武质系列,各岩性岩石的稀土元素配分形式基本一致,均呈轻稀土富集的右倾型。微量元素特征表现为富集大离子亲石元素(Cs、Rb、Ba、Th、U),亏损高场强元素(Nb、Ta、Ti、P)。岩体(87Sr/86Sr)i值为0.704731~0.710280,εNd(t)=-4.49^+0.83。岩浆在冷凝过程中发生了橄榄石-单斜辉石-斜方辉石-斜长石-普通角闪石的分离结晶作用。岩石地球化学特征表明岩体受到同化混染作用。肯得隆岩体的原生岩浆为普通的玄武质岩浆,源自被古生代俯冲熔/流体交代的富集岩石圈地幔。钛铁矿的富集机制是:岩浆在氧逸度低于NNO条件下经历了相对高度的分异演化而最终达到钛铁矿富集。The Kendelong mafic-ultramafic intrusion is located at the Olongbuluke micro-continent,which is in the northern margin of the Qaidam basin,Qinghai Province. The rock types of this fragmentarily outcropped intrusion widely range from serpentinite,clinoperidotite,iherzolite,olivine websterite, olivine clinopyroxenite, olivine gabbro, olivine-bojite, bojite, alterated gabbro to anorthosite. Scatteredly and speckledly disseminated ilmenite ore exists in the pyroxenolite and gabbro. The content of the ilmenite is5% ~ 10%,in some samples it can achieve 10% ~ 20%. Enrichment of ilmenite happened at the late stage of magma evolution. The zircon U-Pb age of the gabbro from the intrusion is 491 ± 3Ma（ MSWD = 0. 7）. According to the geochemical compositions,the intrusion has a tholeiitic affinity. The REE patterns of all rocks have the same characteristics,namely the right slope with LREE enrichment. The complex is characterized by enrichment of LILEs（ Cs,Rb,Ba,Th,U） and depletion of HFSEs（ Nb,Ta,Ti,P）.（87Sr /86Sr）i values vary from 0. 704731 to 0. 710280,εNd（ t） values are between- 4. 49 and ＋ 0. 83. Fractional crystallization of olivine,orthopyroxene,clinopyxene,plagioclase takes place in magma condensation process,and crustal contamination is significant from the evidence of petrochemistry. The primary magma of the Kendelong intrusion is basaltic,which origined from a juvenile lithospheric mantle that was previously metasomatized by subduction zone fluids / melts in the Paleozoic. It may be the highly differentiated magma that achieved the enrichment of the iron titanium oxide. It lead to the formation of the ilmenite deposit in the condition of f O2 〈NNO.

关 键 词：镁铁-超镁铁质岩体 钛铁矿富集 锆石U-PB年龄 富集岩石圈地幔 柴北缘 

分 类 号：P588.124[天文地球—岩石学] P588.125[天文地球—地质学]